The present invention relates to a process for efficiently purifying proanthocyanidin oligomers with high purity which have a variety of biological activities including antitumor, anti-inflammatory, anti-aging, antioxidant, antiallergy, antibacterial, and hair growth activities, and can usefully be applied to foods, cosmetics, drugs or the like.
Generally, proanthocyanidin, which is known as a biophylaxis substance of higher plants, is a generic name for polymers in the form of a dimer or higher order which are polymerized by binding formats, such as 4xcex2xe2x86x926, 4xcex2xe2x86x928, 4xcex2xe2x86x928xc2x72xcex2Oxe2x86x927, with flavan-7-ol as a constitutional unit. These are also called condensed tannins, (xe2x80x9cE. Steinegger and R. Hxc3xa4nsel, Pharmacognosy [1st vol.], Approach to Chemistry and Pharmacologyxe2x80x9d (Translated by Shuji Itokawa et al., Hirokawa Publishing Co.), 204-208 (1977); Porter L. J., Flavans and proanthocyanidins, In: Harborne, J. B. (ed.), xe2x80x9cThe Flavonoids, Advances in Research Science 1986xe2x80x9d, Chapman and Hall, 23-55 (1994)). These are generally called proanthocyanidin because they produce anthocyanidin and turn red by acid treatment. Proanthocyanidins are known to show a variety of biological activities. The activities that have been reported include antitumor, anti-inflammatory, anti-aging, antioxidant, antiallergy, antibacterial, and hair growth activities [Bart Schwitters/Jack Masquelier, xe2x80x9c21st century Biophylaxis Substance OPCxe2x80x9d, translated by Akira Sasaki, Fragrance Journal, 50-135 (1997); Tomoya Takahashi, et al., Journal of Investigative Dermatology, 112, 310-316 (1999)]. Not all the relationships between structure and activity, between these biological activities and the degree of polymerization of proanthocyanidins have been clarified. For example, regarding hair growth activity, dimeric to pentameric proanthocyanidin oligomers (especially dimer and trimer) in proanthocyanidins have been reported to have the highest activity (WO96/00561).
Regarding separation and purification of proanthocyanidins from plant bodies, attempts have been made to separate and purify proanthocyanidins from various plant bodies including grape seeds, pine barks, ginkgo leaves, peanuts, and cocoa beans. Examples of industrial extraction from raw materials in these include the extraction from grape seeds (Japanese Published Unexamined Application No.3-200781,W097/39632, U.S. Pat. No. 5,484,594), pine bark (U.S. Pat. No. 4,698,360,W097/44407) or the like. In the method according to Japanese Published Unexamined Application No.3-200781, a pretreatment is performed by allowing white grape seeds to contact with water at less than 70xc2x0 C., followed by extraction by hot water. The resulting extract is applied to a Sephadex LH-20(trademark) column, and then eluted with 70% ethanol, thereby obtaining proanthocyanidins-containing powder with a purity of approximately 90%. In the method according to U.S. Pat. No. 4,698,360, 1 ton of pinaster bark is subjected to hot water extraction under pressure, and then ethyl acetate elution and precipitation by addition of chloroform are repeated, so that proanthocyanidins-containing powder is obtained. However, none of the purified products resulting from the above methods contains 90% or more of dimeric to pentameric proanthocyanidin oligomers only. All of these purified products also contain monomers, hexameric or higher order polymers, or other organic acids.
As a process for purifying proanthocyanidins using the counter current liquid-liquid distribution method, for example, a method using water and ethyl acetate is described in Andrew G. H. Lea, J. Sci. Fd. Agric., 29, 471-477 (1978), in Japanese Published Unexamined Application No.61-16982 and the like.
As a process for purifying proanthocyanidins using solid-liquid extraction, for example, a method using ethyl acetate is described in Japanese Published Unexamined Application No.8-176137 and EP0707005.For example, 100 kg of crushed grapes are extracted with a mixed solvent of water (1650L), sodium chloride (300 kg) and acetone (550L). Next, acetone is removed by distillation so as to obtain the residue. The residue is then subjected to solid-liquid extraction using ethyl acetate, and then dichloroethane (45L) is added thereto, thereby obtaining 1.5 kg to 2.5 kg of a proanthocyanidin precipitate (EP0707005)
Further, known methods for purifying proanthocyanidins using chromatography include a method using the above Sephadex LH-20(trademark) column (a method for extraction from grape seeds, Japanese Published Unexamined Application No.3-200781), and a method using polystyrene-based adsorption resin (a method for extraction from red beans, Japanese Published Examined Application No. 7-62014). For example, polystyrene polystyrene-based resin xe2x80x9cSepabeads SP-850(trademark) xe2x80x9c(MITSUBISHI CHEMICAL CORPORATION) is added to water obtained by immersing dried red beans therein and the mixture is stirred, thereby allowing proanthocyanidins to adsorb thereto. Then, the resin is dried at less than 70xc2x0 C., and then eluted with 80% (v/v) ethanol at 70xc2x0 C., so that crude proanthocyanidins-containing powder with a purity of approximately 60% can be obtained.
However, all of these processes are for purifying proanthocyanidin mixtures independent of polymerization degree. That is, these processes are not for efficiently and selectively obtaining dimeric to pentameric proanthocyanidin oligomers. Their recovery rate of dimeric to pentameric proanthocyanidin oligomers is low.
Regarding separation of proanthocyanidins by polymerization degree, a method using normal phase silica gel liquid chromatography is known (A method for extraction from cocoa beans: J. Rigaud et al., J. Chromatogr. A, 654, 255-260 (1993), A method for extraction from grape seeds: Corine Prieur et al., Phytochemistry, 36, 781-784 (1994)). The former method comprises loading a sample solution containing proanthocyanidins, which has been obtained by methanol extraction from cocoa beans, into a silica gel column, followed by gradient elution using a mixed solvent of dichloromethane:methaol:formic acid:water [(41xe2x86x925):(7xe2x86x9243):1:1] as a mobile phase. The latter method comprises loading a sample solution containing proanthocyanidins, which has been obtained by methanol extraction from grape seeds, into a silica gel column, followed by gradient elution using a mixed solvent of dichloromethane:methanol:water:trifluoroacetic acid [(82xe2x86x9210):(18xe2x86x9286):2:0.05] as a mobile phase.
However, these methods involve problems such that recovery and reuse of solvents are difficult because of the use of a solvent containing chlorine and the complication of a solvent composition. Further, gradient elution to apply concentration gradients to a mobile phase is required. Therefore, these methods are not appropriate for mass purification-oriented industrial separation methods in view of safety and economy.
The object of the present invention is to provide processes for efficiently purifying dimeric to pentameric proanthocyanidin oligomers with high purity from raw materials containing proanthocyanidins or crude purification products therefrom.
A combination of conventional techniques is not good enough to remove substances other than the target components being dimeric to pentameric proanthocyanidin oligomers, for example monomers constituting proanthocyanidins, such as flavonoids, catechin or epicatechin, hexameric or higher order high polymeric proanthocyanidin polymers, or other contaminants. That is, it is difficult to efficiently obtain with high purity dimeric to pentameric proanthocyanidin oligomers, which are target components of this invention. In addition, most of known methods are not appropriate for industrial processes in view of the complication of a solvent composition used, economy, safety or the like.
As a result of thorough studies to solve these problems, we have completed a process for efficiently purifying dimeric to pentameric proanthocyanidin oligomers with high purity.
The first embodiment is a process for purifying dimeric to pentameric proanthocyanidin oligomers, which comprises extracting the proanthocyanidin oligomers by a solid-liquid extraction method using methyl acetate as a liquid phase from raw materials containing the proanthocyanidin oligomers or crude purification products therefrom.
As the above liquid phase, methyl acetate may be used as a single solvent or a mixed solvent, being a combination of methyl acetate and an organic solvent miscible with methyl acetate, which is prepared by adding such an organic solvent to methyl acetate.
The second embodiment is a process for purifying dimeric to pentameric proanthocyanidin oligomers which comprises pretreating with an enzyme for hydrolysis raw materials containing the proanthocyanidin oligomers, crude purification products therefrom, or a solution containing one of these.
The third embodiment is a process for purifying dimeric to pentameric proanthocyanidin oligomers with a uniform polymerization degree, wherein the proanthocyanidin oligomers are separated and purified by polymerization degree from raw materials containing the proanthocyanidin oligomers or crude purification products therefrom by normal phase silica gel liquid chromatography using as a mobile phase a single solvent or a mixed solvent of two or more solvents selected from the group consisting of an ester solvent, a ketone solvent, a hydrocarbon solvent, an ether solvent and an alcohol solvent. Preferably, a mixed solvent of two or more solvents is used as the above mobile phase.
Further, the present invention can provide purified dimeric to pentameric proanthocyanidin oligomers with a purity of 90(w/w) % or more, dimeric proanthocyanidins with a purity of 90(w/w) % or more, and trimeric proanthocyanidins with a purity of 90(w/w) % or more, which are obtainable by the above purification processes or a combination thereof.
Proanthocyanidins are condensed tannins present in various plant bodies and possess a basic structure wherein flavan-7-ol is sequentially condensed or polymerized by binding of 4xcex2xe2x86x926, 4xcex2xe2x86x928, 4xcex2xe2x86x928xc2x72xcex2Oxe2x86x927 or the like. In this specification, dimers to pentamers of proanthocyanidins and hexamers or higher order polymers of proanthocyanidins are defined as proanthocyanidin oligomers and proanthocyanidin polymers, respectively. Moreover, a flavan-7-ol monomer is defined as a monomer constituting proanthocyanidins. Examples of proanthocyanidin oligomers include proanthocyanidins, such as procyanidin, prodelphinidin, and propelargonidin, and all the stereoisomers thereof. A monomer constituting proanthocyanidins is shown by the following formula (I): 
(wherein R1, R2, R3, R4, R5 and R6 are the same or different and represent hydrogen, a hydroxyl group or a galloyl group).
Examples of raw materials or crude purification products therefrom used in this invention include any which contain proanthocyanidin oligomers, and particularly preferable examples of these include plant raw materials, such as fruits, seedvessels, seeds and barks of plants, extracts therefrom, and crude purification products therefrom. For example, those rich in the content of proanthocyanidin oligomers are preferable, including juice of fruits, or extracts from seedvessels or seeds, of grapes, persimmons, apples, blueberries, cranberries or the like; or extracts from epidermis of peanuts, chestnuts or the like, husks of barley bran or buckwheat, leaves of persimmon, pine bark, palm, or the like.
Furthermore, crude products or crude purification products therefrom obtained by non-enzymatic or enzymatic methods can also be used as raw materials. Examples of a synthetic process for synthesizing proanthocyanidin oligomers include a manufacturing process for a dimer of epicatechin or catechin described in Journal of Chemical Society Perkin Transaction I, 1535-1543 (1983) and a manufacturing process for a trimer of epicatechin or catechin described in Phytochemistry, 25, 1209-1215 (1986). Crude products or crude purification products therefrom obtained by or in a manner similar to these processes can also be used as raw materials for the process of this invention.
A volatile organic solvent is preferable as the organic solvent miscible with methyl acetate used for the first embodiment. Examples of such organic solvents include alcohol solvents, such as methanol, ethanol, propanol, and butanol; ester solvents, such as methyl formate, ethyl formate, and ethyl acetate; ketone solvents, such as acetone; nitrile solvents, such as acetonitrile; ether solvents, such as tetrahydrofuran and 1,2-dimethoxyethane; hydrocarbon solvents such as hexane; and carboxylic acid solvents such as acetic acid. When an organic solvent miscible with methyl acetate is used, the entire extraction solvent preferably contains methyl acetate 50% (volume) or more, more preferably 70% (volume) or more, and still more preferably 90% (volume) or more.
Examples of the enzyme for hydrolysis used in the second invention include glycosidase and esterase.
Examples of the enzyme for hydrolysis used in the second invention include glycosidase, and esterase.
Examples of glycosidase include a single substance or a mixture of two or more substances selected from the group consisting of amylase, cellulase, glucanase, xylanase, glucosidase, dextranase, chitinase, galacturonase, lysozyme, galactosidase, mannosidase, fructofuranosidase, trehalase, glucosaminidase, pullulanase, ceramidase, fucosidase, and agarase. Examples of esterase include a single substance or a mixture of two or more substances selected from the group consisting of carboxyesterase, arylesterase, lipase, acetylesterase, cholinesterase, pectinesterase, cholesterol esterase, chlorophyllase, lactonase, tannase, and hydrolase.
In the second embodiment, examples of the solution containing raw materials containing dimeric to pentameric proanthocyanidin oligomers or crude purification products therefrom generally include an aqueous solution, or an aqueous solution containing 10% or less of an organic solvent, such as an alcohol, ester, or ketone.
In the third embodiment, examples of the ester solvent used as a mobile phase include methyl formate, ethyl formate, propyl formate, isopropyl formate, butyl formate, isobutyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, butyl propionate, isobutyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, isopropyl butyrate, butyl butyrate, and isobutyl butyrate. Examples of the ketone solvent include acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl tert-butyl ketone, diethyl ketone, diisopropyl ketone, methyl vinyl ketone, cyclobutanone, cyclopentanone, and cyclohexanone. Examples of the hydrocarbon solvent include pentane, hexane, heptane, octane, nonane, decane, nonadecane, cyclohexane, xylene, and toluene. Examples of the ether solvent include tetrahydrofuran and 1,2-dimethoxyethane. Examples of the alcohol solvent include methanol, ethanol, propanol, isopropanol, butanol, sec-butanol, tert-butanol and the like.
Extraction and rough purification from plant raw materials can be performed, for example, by known processes as described below.
Plant raw materials including plant fruits, seedvessels, seeds, coats, husks, leaves, and barks are used as materials for extraction after a drying process such as air drying generally. The intact plant raw materials may also be used as materials for extraction.
Rough extraction of proanthocyanidins from the above materials for extraction can be performed with reference to known processes [Chem. Pharm. Bull., 38, 3218 (1990), Chem. Pharm. Bull., 40, 889-898 (1992)]. For example, crushed or shredded plant raw materials are subjected to extraction using a solvent. As the solvent for extraction, a single or a mixed solvent of two or more solvents selected from a hydrophilic solvent and a lipophilic solvent may be used. Such solvents include water, alcohol solvents such as methanol, ethanol and isopropanol, ketone solvents such as acetone and methyl ethyl ketone, and ester solvents such as methyl acetate and ethyl acetate. A temperature for extraction generally ranges from 0 to 100xc2x0 C., preferably 5 to 50xc2x0 C. A material such as a seed which contains oil may be subjected as such to extraction without crushing. Extraction may be repeated two to three times, if necessary. The insoluble residue is removed by filtration or centrifugation from the rough extract solution obtained by the above step, obtaining a rough extract solution. Plant raw materials, such as plant juice, sap or the like, maybe directly used as materials for extraction, or a concentrated rough extract solution of condensed tannins maybe prepared with reference to Agric. Biol. Chem., 45, 1885-1887 (1981).
Extraction and rough purification from rough products obtained by a chemical method, such as non-enzymatic or enzymatic methods, may also be performed in a manner similar to those described above.
Next, a detailed description of the purification process of this invention will be given with examples.
In the first invention, dimeric to pentameric proanthocyanidin oligomers are purified by subjecting raw materials containing the proanthocyanidin oligomers or crude purification products therefrom to solid-liquid extraction using either a single solvent of methyl acetate or a mixed solvent of methyl acetate and an organic solvent miscible with methyl acetate as a liquid phase. When raw materials or crude purification products therefrom are liquid, previous solidification by spray-drying or freeze-drying is preferably performed. Generally, the mixture ratio (w/v) of a solid and methyl acetate, or of a solid and a mixed solvent of methyl acetate and an organic solvent miscible with methyl acetate is approximately 1:1 to 1:1000. Extraction is performed at room temperature or by heating with stirring for a short period of time. Preferably, the mixture ratio (w/v) of a solid and methyl acetate, or of a solid and a mixed solvent of methyl acetate and an organic solvent miscible with methyl acetate is 1:5 to 1:100. Extraction at room temperature for approximately 1 hour, and the subsequent repeated extraction (several times) of the residue under the same conditions are more preferred. A finer particle size of powder is preferred for efficient solid-liquid extraction. When extraction is performed using a mixed solvent, it is preferable that the mixed solvent has solvent polarity analogous to that of methyl acetate by mixing the solvents. The solid-liquid extraction using these solvents suppresses elution of proanthocyanidin polymers and other contaminants, and enables efficient purification of dimeric to pentameric proanthocyanidin oligomers. In the first embodiment, dimeric to pentameric proanthocyanidin oligomers may be recovered by freeze-drying or spray drying after concentrating the resulting methyl acetate extract and dissolving again the concentrated residue in water or in an aqueous solvent such as a buffer.
In the second embodiment, dimeric to pentameric proanthocyanidin oligomers are purified by pretreating with an enzyme for hydrolysis raw materials containing the proanthocyanidin oligomers, crude purification products therefrom, or a solution containing one of these. The raw materials or crude purification products therefrom generally contain many contaminants other than proanthocyanidin oligomers. Particularly, when the raw materials or crude purification products therefrom are derived from plants, polyphenol glycosides, esters or the like, besides proanthocyanidin oligomers, are present in a high proportion. Pretreatment of such glycosides or esters, which are contaminants, with the above hydrolase to obtain aglycon enables efficient removal of the contaminants at the next purification step and improvements in purity of proanthocyanidin oligomers. For example, by treatment with xcex2-glycosidase, rutin, which is a flavonoid glucoside abundant in a whole plant of Fagopyrum esculentum of the family Polygonaceae, results in quercetin being aglycon. When chlorogenic acid and p-coumaroylquinic acid, which are hydroxycinnamates and contained richly in fruits or leaves of dicotyledons, are treated with hydroxycinnamate hydrolase, their depside bonds, which are intramolecular ester bonds, are hydrolyzed, resulting in caffeic acid and quinic acid, and p-coumaric acid and quinic acid, respectively. Reaction conditions for treatment with the enzyme for hydrolysis differ depending on the type of enzymes or the like. Generally, conditions are pH 3 to 8, 25 to 55xc2x0 C., and 1 to 24 hours. The above aglycon components, free sugars or carboxylic acids resulting from treatment with the enzyme for hydrolysis, can be easily removed by conventional techniques such as cooling, liquid-liquid or solid-liquid extraction, or column adsorption, or a combination of these methods and normal phase chromatography. These steps allow efficient removal of contaminants in raw materials containing dimeric to pentameric proanthocyanidin oligomers or crude purification products therefrom, and improvement in purity of the target components, that is dimeric to pentameric proanthocyanidin oligomers.
In the third embodiment, dimeric to pentameric proanthocyanidin oligomers with a uniform polymerization degree can be obtained by separation and purification by polymerization degree from raw materials containing the proanthocyanidin oligomers or crude purification products therefrom by normal phase silica gel liquid chromatography using as a mobile phase a single solvent or a mixed solvent of two or more solvents selected from the group consisting of an ester solvent, a ketone solvent, a hydrocarbon solvent, an ether solvent and an alcohol solvent. To the above normal phase silica gel liquid chromatography, either a method using open column chromatography or that using high performance liquid chromatography can be applied. A solvent or water is removed from the solution containing dimeric to pentameric proanthocyanidin oligomers, and then the residue is dissolved in a mobile phase or in an organic solvent soluble in a mobile phase. When raw materials or crude purification products therefrom are solid, they are directly dissolved in a mobile phase or in an organic solvent soluble in a mobile phase. If necessary, they are filtered through a membrane filter or the like and then charged into a column. Upon elution of a target component, isocratic elution applying no concentration gradient on a mobile phase is preferred in view of simplification of operation. Examples of a preferable mobile phase in isocratic elution include mixed solvents, such as hexane/methanol/ethyl acetate, hexane/acetone, hexane/methanol/tetrahydrofuran/acetic acid, hexane/methanol/tetrahydrofuran/formic acid, hexane/methanol/methyl acetate/acetic acid, hexane/methanol/methyl acetate, and hexane/methyl acetate/acetone.
The purification process of the third embodiment enables efficient removal of contaminants, that is, monomers constituting proanthocyanidins, such as (+)-catechin, (+)-gallocatechin, (xe2x88x92)-epicatechin and (xe2x88x92)-epigallocatechin, and hexameric or higher order proanthocyanidin polymers; and enables separation and purification by polymerization degree of target components, that is, dimeric to pentameric proanthocyanidin oligomers.
The purification processes of the first to third embodiments in the present application may be freely selected, repeated, or combined depending on raw materials to be used as an extraction source, target purity and the like.
To purify dimeric to pentameric proanthocyanidin oligomers, combining two or more purification processes of the first to third embodiments is preferred. To purify dimeric to pentameric proanthocyanidin oligomers with a uniform polymerization degree, combining a purification process of the first embodiment and/or that of the second embodiment, and that of the third embodiment is preferred. Moreover, these processes may be combined with other known processes. When the purification processes are combined, the steps to be used and the order thereof may be freely selected.
By these processes, dimeric to pentameric proanthocyanidin oligomers, dimeric proanthocyanidins, and trimeric proanthocyanidins with highpurity (purity of 90(w/w) % or more) can be efficiently obtained.
Dimeric to pentameric proanthocyanidin oligomers, dimeric proanthocyanidins, and trimeric proanthocyanidins purified by the purification processes of this embodiment can be used as raw materials for manufacturing foods, cosmetics, drugs or the like.